From 5ca0b5a0c5ebf5d9eae2fac53a549bf4d0d06ed3 Mon Sep 17 00:00:00 2001
From: Alex Lorenz <arphaman@gmail.com>
Date: Fri, 17 Mar 2023 18:17:32 -0700
Subject: [PATCH] [interop][SwiftToCxx] ensure we always expose limited set of
 APIs from Swift's standard library to C++

Fixes https://github.com/apple/swift/issues/64340
---
 lib/PrintAsClang/DeclAndTypePrinter.cpp         |  6 +++++-
 .../enums/swift-enum-implementation.swift       | 17 +++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/lib/PrintAsClang/DeclAndTypePrinter.cpp b/lib/PrintAsClang/DeclAndTypePrinter.cpp
index 89ccc75dd1af0..cbde3dd673baf 100644
--- a/lib/PrintAsClang/DeclAndTypePrinter.cpp
+++ b/lib/PrintAsClang/DeclAndTypePrinter.cpp
@@ -2784,8 +2784,12 @@ static bool isExposedToThisModule(const ModuleDecl &M, const ValueDecl *VD,
   if (VD->hasClangNode())
     return true;
   auto *mc = VD->getModuleContext();
-  if (mc == &M || mc->isStdlibModule())
+  if (mc == &M)
     return true;
+  // Only certain declarations are exposed from
+  // the standard library.
+  if (mc->isStdlibModule())
+    return hasExposeAttr(VD);
   return exposedModules.count(mc->getName().str());
 }
 
diff --git a/test/Interop/SwiftToCxx/enums/swift-enum-implementation.swift b/test/Interop/SwiftToCxx/enums/swift-enum-implementation.swift
index fff63ddd617d4..a3e864fbbb957 100644
--- a/test/Interop/SwiftToCxx/enums/swift-enum-implementation.swift
+++ b/test/Interop/SwiftToCxx/enums/swift-enum-implementation.swift
@@ -4,6 +4,9 @@
 
 // RUN: %check-interop-cxx-header-in-clang(%t/enums.h -Wno-unused-private-field -Wno-unused-function)
 
+// RUN: %target-swift-frontend %s -typecheck -module-name Enums -enable-experimental-cxx-interop -emit-clang-header-path %t/enums-default.h
+// RUN: %FileCheck %s < %t/enums-default.h
+
 public enum E {
     case x(Double)
     case y(UnsafeRawPointer?)
@@ -25,6 +28,11 @@ public enum E {
     }
 }
 
+public enum E2 {
+    case foobar
+    case baz
+}
+
 public struct S {
     public var x: Int64
     
@@ -166,6 +174,15 @@ public struct S {
 // CHECK-NEXT: #endif
 // CHECK-NEXT:     vwTable->initializeWithTake(destStorage, srcStorage, metadata._0);
 // CHECK-NEXT:   }
+
+// CHECK: class SWIFT_SYMBOL({{.*}}) E2 final {
+// CHECK: SWIFT_INLINE_THUNK operator cases() const {
+// CHECK: }
+// CHECK-NEXT: }
+// CHECK-EMPTY:
+// CHECK-NEXT: SWIFT_INLINE_THUNK swift::Int getHashValue() const SWIFT_SYMBOL({{.*}});
+// CHECK-NEXT: private:
+
 // CHECK:      namespace Enums SWIFT_PRIVATE_ATTR SWIFT_SYMBOL_MODULE("Enums") {
 // CHECK:        SWIFT_INLINE_THUNK E E::_impl_x::operator()(double val) const {
 // CHECK-NEXT:     auto result = E::_make();